A. Field of the Invention
The present invention relates to an ink-jet head, and especially to an ink-jet head with bubble-driven flexible membrane.
B. Description of the Prior Art
The structure of a conventional bubble-driven ink-jet head is illustrated in FIG. 1. Referring to FIG. 1, the ink-jet head comprises: a substrate 1, a heating layer 2 with a resistor 3 formed on the substrate 1, a dielectric layer 4 formed on the substrate 1, a nozzle plate 5 formed on the dielectric layer 4 having a nozzle 6 formed therein, and an ink chamber 7 formed within said dielectric layer 4 and between the heating layer 2 and the nozzle plate 5 for containing ink, and an ink channel 8 communicating with an external ink cartridge (not shown).
When applied with a voltage pulse, the resistor 3 provides a sudden outburst of thermal energy to cause the adjacent ink to vaporize locally, and creating a bubble in the ink chamber 7. The sudden expansion of the bubble creates a pressure wave in the ink and causes an ink droplet to be expelled from the nozzle 6. Then, when the voltage pulse has vanished, the bubble collapses soon afterwards. Thus, the ink ejections can be generated repeatedly by controlling the application of voltage pulses to the resistor 3.
A problem of the conventional bubble-driven ink-jet head is that it vaporizes the ink directly. In this case, it requires new kinds of ink which must be thermal-stable, of low electrical conductibility, and of low chemical activity. Moreover, when the bubbles are created and collapse near the resistor 3, the impact caused by the bubbles can damage the resistor 3, and the chemical properties of the ink can also cause damage to the resistor 3, thus inevitably reduce the lifetime of the resistor 3. In addition, since the creation and collapse of the bubbles are determined by temperature, rapid heat dissipation is required. Accordingly, when the resistor 3 vaporizes the ink, it has to be cooled down rapidly. Moreover, the printing quality may be impaired due to the ink droplets remained on the outer surface of the nozzle plate after ejection.
To overcome the above-mentioned problems, U.S. Pat. No. 4,480,259 disclosed an ink-jet printer with bubble driven membrane. Referring to FIG. 2, the ink-jet head of the ink-jet printer comprises: a substrate 11; a heating layer 12 with a resistor 13 formed on the substrate 11; a flexible membrane 14 formed on the heating layer 12 and forming a working fluid chamber 15 cooperating with the heating layer 12 to contain working fluid; a dielectric layer 16 formed on the flexible membrane 14 and forming an ink chamber 17 therein; and a nozzle plate 18 formed on the dielectric layer 16 with a nozzle 19 formed therein.
When the resistor 13 is applied with a voltage pulse, the resistor 13 provides a sudden outburst of thermal energy to cause the working fluid to vaporize locally, and creating a bubble in the working fluid chamber 15. The sudden expansion of the bubble increases the pressure within the working fluid chamber 15. The expansion of the bubble causes the flexible membrane to be deformed, resulting in a local deformation of the membrane and the propagation of a pressure wave to the ink in the ink chamber 17. The pressure wave then ejects a droplet of ink from the nozzle 19. By controlling the energy input to the resistor 13, the bubble collapse quickly back onto or near resistor 13 so that repeated operations are feasible.
The advantage of the ink-jet head with bubble driven flexible membrane is that it is not necessary to directly heat the ink. Instead, a selected working fluid is heated. So, it can be used with any kinds of conventional ink and working fluid which do not cause damage to the resistor. However, the prior art still left a few problems unresolved yet including the problems of rapid heat dissipation, and ink droplets remaining on the outer surface of the nozzle plate. In addition, there is still a problem about erroneous operation of ink ejection caused by pressure wave propagation. Each working fluid chamber is communicating with one another via a working fluid channel and thus forming a closed working fluid channel system. In this case, when the working fluid creates a bubble within the working fluid chamber, since the working fluid itself is incompressible, a pressure wave will be transmitted to a neighboring working liquid chamber of an adjacent ink-jet head unit and causes ink droplets to be ejected from wrong ink-jet head units. Moreover, the membrane of the prior art is made of material that cannot prevent of vaporized working fluid and is not made of material durable enough to sustain high frequency operations of ink ejection.